How can I fix this jagged Shadows?
You can increase the size of the Cube texture for the light and check Soft Shadows.

Shadows in EEVEE are created by rendering a depth texture from the light source that are then matched up with the cameras depth texture. It's then possible to see where the depth from the light fails to reach the current pixel. The downside with this technique is it requires fairly high resolution and can still cause a set of unwanted behaviours and artefacts. But that is the price we pay to get crazy fast rendering compared to raytracing.

By using soft shadows EEVEE does a set of these light depth passes at a slight offset that are then used to soften the shadow out a bit. You can adjust the Radius on the light to adjust the smoothing.